Viewports are used in Paper Space to display one or more views of your model. A viewport has two components: a boundary and the view that it contains. You can only insert views that have already been created - see Creating a View.
Note: If you want to insert standard views (views you do not have to pre-define), see Drafting Palette - Creating Standard Views
Typically, multiple viewports are created so that you can show several view of the model. If you make changes to your model, any relevant views in the viewports will automatically update.
Once a viewport is created, you can use 2D tools and annotation tools (Text, Dimensions, Hatching, etc.) to enhance the Paper Space.
You also have the option of saving a viewport's contents as an image. This is handy for rendering objects in viewports, because it is faster to display an image than to render an object. See Cache Properties.